Lightroom Classic 7.1: Import completely broken

Import (or folder sync) has become unusable. I have been using LR since 2.x and have never seen anything like this. LR takes hours for a few hundred files now. The biggest problem seems to be with building previews.

Import from SD card using USB3 reader. About 400 photos from Sony A7RII (42MB each). I had this set to build 1:1 previews, build smart previews, no develop setting (I do usually set one), no copies, no DNG. Either import or folder sync behaved the same way.

I am trying the same import with minimal previews to another folder (don't import suspected duplicates is not selected); it completed in about 5 minutes and now it's progressing with the smart previews. UI is somewhat usable but very sluggish at this point. LR was only using about 4GB of memory, all 8 vCPUs were going about 50% which is not bad.

Destination is a Samsung 1TB 950 SSD; system drive is Samsung 512GB NVMe (cache on this drive, set to 25GB) if that matters. Again, I did reset the preferences last night and also rebooted the system. That didn't change the preview setting to minimal.

Changing this, the overall time for importing 356 images (42MB each) was around 5 minutes. The app goes into "Not Responding" for long periods of time, comes back, screen blacks out, flashes, repeat... Gets "stuck" at 8%, 22%, 49%, After "Copying and Importing" phase, it's building Smart Previews (slowly) but now the app is responding. Building a 1:1 preview (e.g., zooming to 1:1) takes about 15 seconds.

The same dataset with my initial settings was taking well over an hour, maybe closer to 2. That improved somewhat after resetting settings.

I thinking that now simultaneous import (copy) and preview generate mess whole import process. It is also now much related to HDD/SSD speed. Could you add new option to import "Make previews after file copy"?